This invention relates to electrical distribution panelboards, particularly those for use in residential and light industrial applications known as load centers.
Electrical distribution load centers comprise a wall mounted box enclosure. Within the enclosure is mounted an interior panel which supports conductive bus bars and electric circuit breakers attached to the interior and to the bus bars. A dead front cover is disposed over the box with openings for the circuit breaker handles to project through and a door is hinged to the enclosure over the dead front to conceal the circuit breaker handles. A goal in load center design is to reduce the cost of the load center. A common approach has been to reduce the number of fasteners or to eliminate fasteners entirely, thereby reducing labor steps required for assembly.
U.S. Pat. No. 5,181,165 issued Jan. 19, 1993 to D. F. Gehrs et al discloses an insulating support having slots in lateral edges into which bus bars are inserted from the opposite edges toward a center of the support. Interfitting retention means are provided on the bus bars and the support to function as detents for retaining the bus bars assembled to the support. The support is also provided with a plurality of integrally molded pins projecting from a back side of the support which extend through holes in a fiber insulator board and in a sheet metal pan of the interior panel. The pins are ultrasonically staked at the back side of the pan to retain the support and bus bars permanently assembled to the sheet metal pan. This approach eliminates separate fasteners such as screws or rivets, but still requires a separate fastening operation ultrasonically staking the pins on the back side of the pan.
U.S. Pat. No. 5,134,543 issued Jul. 28, 1992 to J. O. Sharp et al discloses an electrical load center wherein the interior panel comprises a molded insulating support panel for the bus bars which also has mechanical attachment means for the circuit breakers incorporated in the molding. Accordingly, the molded insulating support of Sharp et al incorporates the features of the separate metal pan to reduce the number of individual parts. The bus bars are attached to the back side of the molded insulating support by inserting one end in a molded pocket and pivoting the other end into engagement with a resilient snap hook integrally molded in the support. The patent also discloses several short supporting walls arranged on opposite sides of the bus bar in the support panel which are ultrasonically staked over the bus bars to retain the bus bars in place as an alternate or a conjunctive construction to the snap-in mounting of the bus bars. The structure for mechanically attaching the circuit breakers to this support panel comprises parallel rows of double apertures in the front face of the support panel and depending fingers at the back side of the support panel adjacent each of the apertures for receiving two pairs of contact jaw shrouds depending from the molded case of the electric circuit breaker. Only one of the pairs of jaw shrouds has electric contact jaws therein for engaging the respective bus bar. The other pair of jaw shrouds serves solely as a mechanical attachment of the opposite end of the circuit breaker to the support panel. This support panel design requires a wholly new design housing for the circuit breaker to incorporate the two pairs of jaw shrouds which are not usually found on residential and light industrial circuit breakers.
While the above described examples of insulating support panels for load centers are satisfactory for their intended purpose, this invention relates to improvements thereover.